In the field of boat stacking there is an increasing attention to optimizing storage space. Accordingly, in storage facilities are more and more used racks in which the boats are longitudinally stores with the head on the back side and the stern on the front side, resting side by side and one on top of the other on several levels so that the overall plant dimension of the storage facility is minimized. Still for minimizing the overall dimension two of such rack-like storage facilities face each other with a central passage sized so that lift trucks that have to lift boats from the water, carry them and stack them into their racks are able to run into the passage and to manoeuvre.
As it can be easily guessed the main features required to such vehicles are high loading capacity, stability and easiness of manoeuvring both during lifting and stacking operations and during transporting operations. Obviously, a relevant weight and dimension of this trucks positively affects their loading capacity and stability but it reduces the manoeuvrability, in particular as regards the ability of entering the passage between the racks and inside that passage. Furthermore, a relevant dimension means little versatility as small boats are inefficiently transported with large trucks. Finally, a bulky truck could be not admitted to pass onto some surfaces that have a load limit.
The most common lift truck for lifting and stacking boats comprise a lift assembly made of an upright mast bound to the fore section of the vehicle supporting a pair of forks extending in a fore direction of the vehicle. The forks can be raised and lowered with respect to the ground level so that the truck is able to pick up the boat from the water while it rests on a step floor of a pier or a wharf which usually are one meter or more above the water level. In addiction, the forks can be moved closer or apart each other, so that they fit the shape and dimension of the boat's keel. In the back section of the truck is placed a counterweight intended to balance the weight of the boat. It is easily comprehended that the more is the distance of the counterweight from the fore axis of the truck, the more is the loading capacity of the truck. So, in the above trucks, the more is the size and weight of the boat to be lifted, the more will have to be the size and weight of the truck. Obviously, since the boat is overhanging on front of the truck, the total length during the transport operation, which is substantially the sum of the boat length and the truck length without the forks, is very relevant and it creates problems in manoeuvring the truck and large passages between the racks are needed.
The above problems are at least partially fixed by a vehicle as described in U.S. Pat. No. 6,027,303 A in which a self propelled main frame on wheels comprises a pair of parallel rails extending in a fore-and-aft direction on which slides the lifting assembly mounting the forks, and, together with it, also the operator's cab slides. When the boat has to be picked up from the water the lifting assembly is moved at the fore section of the vehicle while during the transport operation and the stacking operation within the passage between the racks the lifting assembly is kept close to the back section of the vehicle so that the centre of gravity of the boat is comprised between the axis of the for wheels and the axis of the rear wheels and a counterweight is no more needed. In this case the total length during the transport operation is just a little greater than the length of the boat so that a greater manoeuvrability is obtained.
In WO 2008/051991 A it is proposed a lift truck for boats which has a frame structure similar to the one above mentioned and which has additional functions that are able to further increase its manoeuvrability, both concerning the space required for manoeuvring and the visibility during the boat transporting and stacking operations. In fact, this last vehicle is provided with four independently steering wheels having a steering angle of 90° so that the vehicle is able to perform a lateral translation movement which is useful when manoeuvring the truck in the passage between two racks. In addiction, the operator's cab is rotatable about a vertical central axis and it can be also lifted, so that the overall dimensions of the boat can be better perceived by the operator when the boat itself is lifted.
Nevertheless, due to the importance of optimizing the storage space in boat storage facilities it is strongly felt the need of searching solutions of boat stacking trucks that at a same loading capacity have little overall dimensions, that are lighter and that require little space for manoeuvring.